Many buildings of all types have large, continuous spans of glass at the outside wall referred to as curtainwall, storefront systems or ribbon windows. Room partitions at the outside wall are usually run into mullions (vertical, thin metal tubes that hold the glass in place) rather than into the glass itself. The joint between the mullion and partition has a gap, or sound flanking path, due to movement of the exterior glass wall relative to the interior partition. This gap lets sound pass between rooms on either side of the partition, which ultimately defeats the purpose of the wall. In addition, lease agreements often prohibit tenants (and their contractors) from connecting drywall partitions to the mullions.
The STC Mullion Seal closes this gap to prevent sound from traveling and enhances acoustical comfort in spaces with these exterior glass walls.